Studies In Animal Locomotion: VII. Locomotory Reflexes In The Earthworm

1. In the absence of longitudinally applied tension, an intact or decapitated earthworm only exhibits peristalsis so long as its ventral surface is in contact with the substratum. 2. The reflex response of a decapitated earthworm to mechanical tension depends upon the precise conditions under which the stimulus is applied. When the muscles of a segment are responding to stimuli which reach them from the efferent tracts in the nerve cord, they are simultaneously being exposed to mechanical tension (due to movements of the muscles of anteriorly situated segments) of such a nature as to cause a reflex response identical in nature to that induced directly by the nerve cord. It is suggested that tension reflexes are chiefly of functional significance when the animal is moving over an irregular surface. 3. During normal peristalsis the nerve cord of an earthworm exhibits an electrical rhythm whose frequency is identical with that of the muscular rhythm. The isolated nerve cord may exhibit an electrical rhythm for prolonged periods, but it is uncertain how far this phenomenon bears any relationship to the muscular rhythm displayed by the intact animal. 4. Peristalsis can be elicited in an inactive decapitated preparation by making the anterior end electropositive to the posterior end. Peristalsis is inhibited by reversing the direction of flow of the current.